The present invention relates to brake shoe assemblies for railroad cars and particularly to spring-type brake shoe locking keys that are adapted to removably affix a brake shoe to its brake head.
Shown in FIG. 1 is one design of a brake shoe locking key adopted by the Association of American Railroads (A.A.R.) as an alternate standard for the standard tapered key. Studies have shown the tapered key to be subject to accelerated wear, which results in loss in its ability to firmly affix the brake shoe to its backing plate. As is well-known, any looseness at the brake shoe/brake head interface results in undesirable brake head wear due to vibrations typically encountered in railroad service. The alternate standard brake shoe key shown in FIG. 1 is made of spring steel and firmly holds the brake shoe to the brake head under tension of the spring load created in the locking key as the key is deformed when driven into its locking position. This spring tension of the locking key takes up play between the brake head and shoe, to prevent the brake shoe backing plate from impacting the brake head in the face of such vibration as would otherwise cause such impact forces to rapidly wear the brake head and brake shoe key bridge.
A disadvantage of this spring-type key is the difficulty encountered in attempting to remove the key when the key has been driven fully into its locking position beyond the initial locking position shown in FIG. 1. A pry bar is typically employed by railroad personnel to force the key out of its locking position by wedging the pry bar between the head of the key and the brake head. In the fully driven locking position of the brake shoe key, however, the key head abuts the brake head, making it difficult to wedge a pry bar therebetween. For this reason, railroad personnel have been prone to drive the brake shoe key short of its locking position, in order to facilitate subsequent removal of the key.
While the foregoing practice assures that the head of the key is spaced sufficiently from the brake head to accommodate the insertion of a pry bar therebetween, failure to at least drive the key into its initial locking position results in the brake shoe being affixed to the brake head with less than sufficient force to prevent vibration from causing impact wear of the brake head and brake shoe key bridge.
This problem was addressed in another alternate standard brake shoe key in which the head of the key is modified in such a manner as to provide a stop with the brake head that establishes a space therebetween in which a pry bar may be inserted to facilitate removal of the key. This key stop is formed by bending the end of the key head in a downward direction so as to form a tab that overlays the key shank in spaced, parallel relationship therewith. This bent over tab is intended to abut the brake head so that the key head proper is spaced therefrom a distance sufficient to accommodate insertion of a pry bar when the key is driven to its full locking position. Due to different designed brake heads, however, the tab on the key head does not always find a stop until the key head abuts or nearly abuts the brake head. Consequently, the intended space in which a pry bar may be inserted between the key head and brake head either does not exist or is so small as to make it difficult to find an effective insertion point for the pry bar. Therefore, this key has not found general acceptance in the industry.